1. Technical Field
The present disclosure relates to a completely automated public turing test to tell computers and humans apart (CAPTCHA).
2. Background Art
CAPTCHA was suggested by Luis von Ahn, and refers to a public turing test that determines whether a user is a human or a computer. Such a CAPTCHA presents a question that can be easily solved by a human, but cannot be solved by a computer, which has been used for authenticating a user in various fields such as an online vote, a free e-mail registration, and an online community registration. The CAPTCHA can use text, image, sound or logic questions, but text-based questions have been mainly used because of their easy implementation, as shown in FIG. 1. As illustrated in FIG. 1, the text-based CAPTCHA displays a modified text, and asks what the displayed text is.
In the case of the currently used text-based CAPTCHA, when a text is severely modified, even a human cannot identify the text, so the text should be modified to an appropriate extent. However, as the text is basically modified in two dimensions, there is a limit in modification.
Further, the text-based CAPTCHA can be incapacitated by an AI technique, and has low accessibility.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.